Multi-stage AP mechanical pulping with refiner blow line treatment

ABSTRACT

The invention combines the step of adding chemicals such as alkaline peroxide to an intermediate line after refining, with the step of applying chemicals such as alkaline peroxide as a pre-treatment before primary refining and/or applying chemicals such as alkaline peroxide at the primary refiner. This is implemented in the preferred embodiment, by pre-treating feed material, refining the materials into a pulp in a superatmospheric refiner, and adding chemicals in the post refining blow-line.

REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation-in-part ofInternational Application No. PCT/US0223078 under 35 U.S.C. §365(c)filed Jul. 19, 2002 (designating the U.S.) which claims benefit under 35U.S.C. § 119(e) of U.S. Provisional Application No. 60/306,974 filedJul. 19, 2001.

FIELD OF THE INVENTION

[0002] The present invention relates to a process for the production ofpulp from lignocellulosic material, such as wood chips or the like, bychemical-mechanical refining.

BACKGROUND OF THE INVENTION

[0003] Applying alkaline peroxide chemicals in a mechanical pulpingsystem (APMP) may be traced back as early as 1962. Since then, therehave been a number of different process ideas developed to apply thechemicals before or during early stages of refiner pulping. In recentyears, an extensive and systematic investigation has been reported onhow different chemical treatments in refiner mechanical pulping affectpulp property development and the process consumption. For hardwoods, itwas observed that alkaline peroxide pretreatment in general gives betteroptical properties, better bleachability and higher pulp yield atsimilar strength properties when compared to other conventional chemicalpretreatment, such as alkaline sulfite and cold caustic soda processes.When compared to a peroxide post-bleaching process, applying alkalineperoxide before refining has a tendency to give a higher bulk at a giventensile strength for some hardwood species, such as North Americanaspen.

[0004] In a very broad sense, alkaline peroxide refiner mechanicalpulping is a type of pulping process where hydrogen peroxide and alkaliin various forms, together with various amounts of different peroxidestabilizers, are applied to the lignocellulosic materials before orduring defiberization and fibrillation in a refiner. In the early stageof development of this type of pulping process, two basic concepts weretried. One was to apply alkaline peroxide treatment on chips, to allowthe bleaching reactions to complete or to approach completion beforerefining. The other basic concept was to apply all the alkaline peroxideat the refiner, either with no pretreatment or with stabilizers or otheralkaline pretreatment prior to the alkaline peroxide application at therefiner.

[0005] Conventionally the inclusion of chemicals such as silicates priorto the refiner leads to a situation where scale forms on the processingequipment. The refiner area itself also can suffer due to the formationof silicate precipitates, especially in processing softwoods, which canlead to a glassing of the refiner plates.

[0006] The application of chemicals at a point downstream of the refinerhas also been proposed. However these proposals did not encompass theuse of chemical pretreatment or conditioning of the chips. In additionsuch downstream chemical addition appeared incompatible with highpressure refining conditions.

SUMMARY OF THE INVENTION

[0007] The present invention is directed to the introduction ofchemicals to lignocellulosic material immediately after refining inorder to achieve, among other things, a comparable bleaching efficiencyas when applying chemicals at locations upstream of and/or at therefiner.

[0008] The introduction of chemicals downstream of the refiner, whereinthe refiner may be a primary, secondary and/or tertiary refiner, isutilized with the concept of applying chemicals such as alkalineperoxide pre-treatment to lignocellulosic material before refining.Preferably, the refiner has a highly pressurized case, for achieving theknown benefits of high pressure refining.

[0009] The introduction of chemicals downstream of the refiner accordingto the invention may alternatively be utilized with the process referredto herein as P-RC (Preconditioning followed by Refiner Chemicaltreatment) for APMP, which combines the concept of applying chemicalssuch as alkaline peroxide as a pretreatment to lignocellulosic feedmaterial before primary refining with the concept of applying chemicalssuch as alkaline peroxide at the primary refiner.

[0010] The preferred embodiment of the invention includes applying morethan one-third of total alkaline peroxide (and/or other chemicals knownin the art to bleach or otherwise process lignocellulosic material intopulp or precursors of pulp) at or near the blow valve in the postrefiner intermediate line, in combination with chemical addition at therefiner and chemical impregnation of the chips upstream of the refiner,to yield a more energy efficient process and to allow a more efficientbleaching than the application of all the chemicals before dischargefrom the refiner.

[0011] A significant benefit of the invention is better chemicalefficiency, by moving a greater number of chemical reactions downstreamrelative to conventional techniques, resulting from the relativelyheavier or more intense addition of chemicals and/or chemicalstabilizers at the post refiner blow line.

[0012] A further benefit of the invention is the reduction in thedetrimental effects of the high temperature and/or other conditionsprior to and during high pressure primary refining, which are known toinfluence pulp brightness and development.

[0013] Another benefit of the invention as implemented in ahigh-pressure system, is the recovery of more and higher quality ofsteam and/or heat than in other types of P-RC APMP systems, where theprimary refiner is either completely atmospheric or atmospheric at theinlet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The invention will be better understood by reference to theaccompanying drawings in which:

[0015]FIG. 1 is a block diagram depicting the general P-RC APMP process.

[0016]FIG. 1A is a block diagram depicting steps of transferringlignocellulosic material to a refiner having a casing at atmosphericpressure, with discharge at atmospheric pressure.

[0017]FIG. 1B is a block diagram depicting steps of transferringlignocellulosic material to a refiner having a pressurized casing withpressurized discharge.

[0018]FIG. 1C is a block diagram depicting steps of transferring primarypulp produced in the refiner with a casing at atmospheric pressure, to ahigh consistency tower via a transfer device.

[0019]FIG. 1D is a block diagram depicting steps of transferring primarypulp produced in the refiner with a casing at atmospheric pressuredirectly to a high consistency tower.

[0020]FIG. 1E is a block diagram depicting steps of transferring primarypulp produced in the refiner with a pressurized casing, to a highconsistency tower via a transport device.

[0021]FIG. 1F is a block diagram consistent with an embodiment of theinvention, depicting steps of transferring primary pulp produced in therefiner with a pressurized casing to a high consistency tower.

[0022]FIG. 2 is a table comparing P-RC with two prior art processes.

[0023]FIG. 3 is a graph of freeness as related to energy consumption forP-RC and two prior art processes.

[0024]FIG. 4 is a graph of density as related to energy consumption forP-RC and two prior art processes.

[0025]FIG. 5 is a graph of the tensile of tensile development for P-RCand two prior art processes.

[0026]FIG. 6 is a graph of burst development for P-RC and two prior artprocesses.

[0027]FIG. 7 is a graph of brightness development for P-RC and two priorart processes.

[0028]FIG. 8 is a graph of the light scattering coefficient of the pulpas a function of freeness for P-RC and two prior art processes.

[0029]FIG. 9 is a comparative table of atmospheric versus pressurizedcasing processing of aspen wood chips according to P-RC.

[0030]FIG. 10 is a comparative table of atmospheric versus pressurizedcasing processing of birch wood chips according to P-RC.

[0031]FIG. 11 is a block diagram consistent with an embodiment of theinvention, depicting steps of transferring primary pulp produced in arefiner with a pressurized casing to a retention tower with a chemicaladdition in the intermediate line following the control valve.

[0032]FIG. 12 is a block diagram consistent with an embodiment of theinvention, depicting steps of transferring primary pulp produced in therefiner with a pressurized casing to a retention tower with an alkalineperoxide chemical addition in the intermediate line prior to the inletof the separator.

[0033]FIG. 13 is a block diagram consistent with an embodiment of theinvention, depicting steps of transferring primary pulp produced in therefiner with a pressurized casing to a retention tower with an alkalineperoxide chemical addition in the intermediate line at the separator.

[0034]FIG. 14 is a block diagram consistent with an embodiment of theinvention, depicting steps of transferring primary pulp produced in therefiner with a pressurized casing to a retention tower with an alkalineperoxide chemical addition in the intermediate line at the separatordischarge.

[0035]FIG. 15 is a comparative table of refiner eye versus blow linechemical addition processing of birch and maple wood chips according tothe invention.

[0036]FIG. 16 is a comparative table of refiner eye versus blow linechemical addition processing of spruce and red pine wood chips accordingto the invention.

[0037]FIG. 17 is a comparative table of refiner eye versus blow linechemical addition processing wood chips at higher pressure according tothe invention.

[0038]FIG. 18 is a block diagram consistent with an embodiment of theinvention, depicting steps of transferring pulp produced in apressurized refiner via a intermediate line to a tower.

DETAILED DESCRIPTION OF THE INVENTION

[0039]FIG. 1 presents a simplified process flow diagram of the P-RCalkaline peroxide mechanical pulping (APMP) process. The P-RC processgenerally applies alkaline peroxide chemicals at chip pretreatment/chipimpregnation step(s)/stage(s) 1, 2 and as the material is fed to theprimary refiner 3.

[0040] The preconditioning step(s) as implemented in stages 1 and 2 ofFIG. 1, preferably include one or two atmospheric compression devices,such as screw presses. Chip material is fed through an inlet, and passesthrough at least one compression region and at least one expansionregion, and is discharged. A chemically active solution (pretreatmentsolution) is added to the material, typically while decompressing ordecompressed at or near the discharge to facilitate penetration of thesolution into the material.

[0041] The refining step 3 may include a primary refiner of conventionalsize, configuration, and operating conditions as known forchemi-mechanical pulping. Depending on such factors as whether chemicalsare to be added and what types of chemicals if any are to be added thesize, configuration, and operating of the refiner can be tailored so asto not expose the chemicals to excessive temperature or time-temperaturecombination. In one embodiment of the invention the pressure can bewithin a range of about 15 psi to pressures greater than 45 psi. Anychemicals added at the refiner will be referred to as the refinersolution.

[0042] Steps implemented following the primary refining, may have alevel of chemical presence carried downstream from the refiner or otherupstream processing. In one embodiment of the invention, the postrefining chemical environment is modified by an addition or additions ofa intermediate line solution or solutions to the intermediate line. Theintermediate line is located between the refiner and the retentiontower. For instance, as shown in FIG. 11, alkaline peroxide solution isapplied to pulp in the intermediate line, at the blow line 30, afterexposure to and discharge from the refiner. The chemicals may be appliedat a point or points along and about the blow line 30. The blow line 30may extend between the blow valve and a separator of the intermediateline. As shown in FIG. 18, the chemicals may also be applied in theintermediate line immediately after the blow valve 40, between the blowvalve and the separator 42 immediately prior to separator 44, at theseparator 46 and/or immediately after the separator 48. The separator,for instance a cyclone, may operate to separate steam/heat/liquid orcombinations of those items from the pulp. Prior to entry into theseparator the pulp may have a consistency of about 20% to about 60% anda temperature of about 80° C. to about 155° C.

[0043] Injection of the chemicals at a intermediate line location orlocations may be made through simple orifices in the intermediate lineand/or by the use of injectors, such as nozzles, associated with theline. The nozzles can be associated with the intermediate line invarious ways along and about the intermediate line to desirably controlthe chemical addition. The control can be dependent, for example, on theeffect that the additions have with regard to the bleaching processand/or conditioning process. Chemical profiles within the pulp flow canthus be modified or maintained by, for example, injection sequencing,flow rate, composition, and/or duration. Other variables such as thedepth of injector intrusion into the flow path, injector angle, injectororifice configuration, and other properties of the injector installationmay be modified to achieve a desired result. Chemical introduction maybe modified by varying the introduction location based on the pressureused in refining. For instance, alkaline peroxide chemicals may beintroduced immediately (from less than a few inches to a few feet) afterthe blow valve, especially in low pressure refining where the pressureis less than about 45 psi. The alkaline peroxide chemicals may also beintroduced immediately before the cyclone (from less than a few inchesto a few feet) after the blow valve, especially in high pressurerefining where pressures higher than 45 psi are used. In other cases thealkaline peroxide chemicals may be introduced intermediate the cycloneand the blow valve, or even at the cyclone.

[0044] The refiner may be primary, secondary, and/or tertiary, with apressurized casing or fully pressurized from preheater to refinerdischarge. The pressure in the refiner aids in expelling the pulp fromthe refiner during discharge. The discharge can be modified orcontrolled by, e.g., the blow valve. The pressure assisted discharge ofthe pulp into the intermediate line can result in the pulp having aresidence time of a few seconds to minutes in portions of theintermediate line. The pulp can achieve high velocities and experiencesignificant turbulence as it flows through the intermediate line. Theseconditions enhance the mixing between the chemicals and the pulp. Theintensive turbulence and a high temperature gradient in the pulp streammay also assist in transferring the chemicals to individual pulp fibersas well into the fiber wall.

[0045] As an illustrative example, the pulp may be about 100° C. orhigher, and the chemical liquor may be 40° C. or lower. The intermediateline solution may preferably be in the range of about 10° C. to about25° C. but can be up to 80° C. The application of alkaline peroxidechemicals at the intermediate line reduces the exposure time of thealkaline peroxide chemicals to high temperature, especially whenelevated temperature and/or pressure is present at refining. This postrefining addition to the pulp flow through injection proximity,facilitates an easier stabilization and an increased efficacy of theperoxide. The use of the invention in an intermediate line with asuperatmopheric refiner system also can result in the enhanced ormodified recovery of steam/heat/liquid from the pulp. Such steam may bediverted away through a steam pipe 36. These features also allow for theproduction of high-freeness pulps with low shives content, since it iswell known in the industry that the higher refining pressure tends toproduce lower shives, or cleaner pulp. In some cases a press may beincluded in addition to or in place of the cyclone 32. The press couldallow for an increase in steam/heat/liquid recovery from the pulp.

[0046] In one embodiment of the invention the optimizing process toinfluence peroxide efficiency and brightness development can beaccomplished when the primary refining is fully pressurized. In oneparticular configuration this may be referred to as P-RC APTMP, whichdiffers from other P-RC APMP configurations where the primary refiner isoperated either under completely atmospheric pressure, or withatmospheric pressure at the inlet and low pressure at the casing.

[0047]FIGS. 1A through 1F present various examples of a P-RC 20 processof the type generally shown in FIG. 1. For example, FIGS. 1A and B showthat after the material is pretreated at 1 and/or 2, addition of thesolution to the lignocellulosic material may more specifically occur ata cross conveyer 10, downstream of the screw press and near refiner 3,or at the refiner itself, e.g., the ribbon feeder 12, the inlet eye ofthe refiner disc 14, and/or at the inlet zone of the plates on therefiner disc 16. As used herein, chemical addition “as the material isfed to the refiner”, encompasses the locations 10, 12, 14, and 16. Therefiner in a P-RC process may have an atmospheric casing 3A or anoverpressure casing 3B, but the inlet to the refiner would normally beat atmospheric pressure. The discharge from a pressurized casing 20 a ofprimary pulp may be through a blow valve or similar device, anddischarge from an atmospheric casing 20 may be by gravity drop or thelike. The discharge from the refiner will, in any event, directly orindirectly go to a high consistency-bleaching tower 24 of any type knownin the art (but subject to temperature control).

[0048] In one embodiment of the invention the pretreatment solutions,the refiner solutions (if present), and the intermediate line solutionsact chemically on the lignocellulosic material. It may be advantageous,depending on the lignocellulosic material and the processing equipment,to modify the chemical exposure profile of the material to the chemicalagents in order to optimize the process, and/or eliminate or reduceunwanted chemical effects or degradation. Such chemical profilemodification may be accomplished by sequential chemical additionsthroughout the process, and can be combined with other variableconditions such as temperature, concentration, pressure, and duration tofurther enhance the desired effect.

[0049] Lignocellulosic material processed using the P-RC process can bedischarged 4 from the primary refiner casing (either atmosphericdischarge 20 or overpressure discharge 20 a), as a primary pulp having ameasurable freeness and could properly be called a pulp able to form ahandsheet. As shown in FIGS. 1C and D, atmospheric discharge from therefiner could pass via a transfer device 22 such as a transfer screw, tothe tower 24, or more directly 28 via a chute or the like. As shown inFIGS. 1E and F, with a pressurized casing the refined pulp wouldtypically be discharged through a blow valve and delivered eitherdirectly or indirectly to the tower. Optionally, as shown in FIGS. 1Cand E, the bleached pulp exiting the tower can be further processed in,e.g., a secondary refiner. The high consistency retention tower 24allows the chemical bleaching reactions carried over from upstream ofthe tower to continue.

[0050] In one embodiment of the invention, for example as shown in FIG.18, the discharge from the blow valve may be delivered indirectly to aretention tower through a seperator and/or a press.

[0051] The presence of an ample amount of the alkaline peroxidechemicals in the primary refiner (e.g., as by shifting a largeproportion of the chemical reactions to the refiner chemical treatmentstage) improves efficiency. This is because variations in chip forms andquality, in addition to the natural heterogeneity of wood chips andfibers, often make it difficult, if not impossible, to achieve a goodchemical distribution in the chip pretreatment/impregnation stage(s). Inthese situations, the mixing action at the primary refiner helps topromote chemical distribution, and hence, improves the chemicalefficiency.

[0052] In accord with one embodiment of the invention, the addition ofchemicals into the post refining intermediate line allows, for example,the use of a pressurized refiner and higher temperatures in refining.Addition of chemicals to the intermediate line at, for example, the blowline provides for a fast, and more direct, distribution of chemicalssuch as peroxide to the chromophore sites for efficient bleaching. Thisefficiency is achieved because the targeted peroxide reactions arecarried out at the reaction site of interest quickly without lengthyexposure to the more heterogeneous environment present in previousportions of the process. Conventionally the temperature at the inletbetween the plates of a refiner pushes the chromophore removal andhemicellulose alkali reactions so fast that that pH is loweredprematurely. Using the post refiner intermediate line as the locationfor chemical mixing according to an aspect of the present invention,distributes the chemicals fast enough, to compete favorably against andcounter to a significant extent, the elevated temperature of the pulp.Such elevated temperature can be, for example, from about 80° C. toabout 155° C.

[0053] In one embodiment of the invention, the pulp can be maintained inan interstage high consistency retention tower. The pulp in the highconsistency retention tower may have a consistency of about 20% to aconsistency of about 40% consistency, with a preferable consistency ofabout 30%. The temperature of the pulp in the high consistency retentiontower may be from about 60° C. to about 95° C. The pulp can be held inthe retention tower from about 30 minutes to more than 2 hours dependingon the chemical reaction needed for chemical treatment. The maintenanceconditions include but are not limited to temperature, pressure, pH,chemical concentration, solids concentration, and time, that allow forconditioning and/or bleaching of the pulp to continue and limit thedegradation of the bleaching agent through reactions that are extraneousto the bleaching of the pulp. Such extraneous reactions may benon-productive, inefficient, and/or harmful to the bleaching of thepulp. Control of some and/or all of the conditions may or may not beneeded depending on e.g., the type and condition of the lignocellulosicmaterial used in the process, and the type, size and operatingenvironment of the equipment itself. For example, conditions oftemperature may be modified throughout the process by the addition ofthe chemicals, pressurized gas, and other heating or cooling methods.Temperature modifying means may be employed during transfer of theprimary pulp 22 by using a mixing screw with water added while the pulpis mixed and transferred to the tower. The temperature of the primarypulp may also be thermally adjusted within the tower if the primary pulpis discharged directly to the tower 28, by means known in the art. Forexample, the pulp may be thermally adjusted through addition of liquidsor gases, and/or through use of heat transfer components such as tubing,tower jacketing, etc.

[0054] As used herein, the term “control” should be understood asincluding both active and passive techniques. Thus, control could beimplemented by a static hardware configuration or by continuallymeasuring one or more process parameters and controlling one or moreprocess variables.

[0055] The chemical conditions present anywhere in the inventive processmay be modified by additives to prevent extraneous degradation. Thismodification may be made at, by way of example, the pretreatment step(s)1 and/or 2, the cross conveyer 10, the ribbon feeder 12, the inlet eyeof the refiner disc 14, the plates of the refiner disc 16, the blowvalve 20 a, the blow line 30, the separator, 32, and/or after theseparator. An example of stabilizers would be chelation agents. Achelation agent refers to a compound that has an ability to formcomplexes, so called chelates, with metals occurring in thelignocellulosic material, and primary pulp. Such metals may includemonovalent metals sodium and potassium, earth-alkali divalent metalscalcium, magnesium and barium, and heavy metals such as iron, copper andmanganese. The metal ions retained in the material as it is processedmakes the bleaching by oxygen chemicals (such as hydrogen peroxide) lesseffective, and results in excess chemical consumption as well as otherproblems well known in the art. In order to reduce or eliminate theeffect of these metal ions on the process, chelants such as for examplediethylene triamine pentaacetic acid (DTPA), ethylene diaminetetraacetic acid (EDTA) and nitriletriacetic acid (NTA) may be used.These and other chelation agents known in the art may be used alone orin combination as needed or desired depending on process conditions. Inaddition, silcates and sulfates as examples may also be usedadvantageously as stabilizers as well as serving other functions wellknown in the art.

[0056] Further embodiments and aspects of the invention will be apparentfrom the examples and description set forth below.

ILLUSTRATIVE EXAMPLES EXAMPLE SET A

[0057] Several general series of pilot plant processes are illustratedin the following examples. The materials and conditions for thefollowing examples, unless specified otherwise are:

[0058] Wood: A blend of 50% aspen and 50% basswood was used in thisstudy. The aspen woods had rotten centers, which made it more difficultto bleach than normally expected. The woods were all from Wisconsin USA,and debarked, chipped and screened before further processing.

[0059] Chemical Impregnation: Chips were pre-steamed first for 10minutes, and then pressed using an Andritz 560GS Impressafiner at 4:1compression ratio before impregnated with alkaline peroxide chemicalliquor. The chemical liquor was introduced at the discharge of thepress, and allowed for 30 minutes retention time before refining.

[0060] Refining: An Andritz 92 cm (36″) Model 401 double discatmospheric refiner at a conventional speed of 1200 rpm was used for allthe refining processes. There was 15 minutes or more retention timebetween the primary and the secondary, and no dilution after the primaryand before the secondary. The refining consistency was 20% at both theprimary and the secondary.

[0061] Pulp Testing: Tappi Standards were used for all pulp testingexcept for freeness, which follows Canadian Standard Freeness (CSF) testmethods.

[0062] In the first of three processes compared, all of the alkalinechemicals were applied, (3.3% total alkalinity, (TA), and 2.4% H₂O₂,together with 0.2% DTPA, 0.07% MgSO₄ and 3% Na₂SiO₃) at the chipimpregnation (preconditioning or pretreatment) stage, (only one stagechip impregnation was applied), then refined at atmospheric pressure.This series was, therefore, named “Chip”. The second series usedapproximately two thirds of the total alkaline peroxide chemicals, (or2.4% TA, 1.6% H₂O₂, 0.08% DTPA, 0.04% MgSO₄ and 2.4% Na₂SiO₃), at thechip impregnation stage, and approximately one third of the totalchemicals, (1.0% TA, 1.0% H₂O₂, 0.19% DTPA, 0.05% MgSO₄, and 0.9%Na₂SiO₃), at the eye of the primary refiner. It is labeled as“Chip+Refiner”, and represents the invention. In the third series,labeled “Refiner”, the chips were first pressed using the same chippress as the first two series, and then all the alkaline peroxidechemicals, (4.2% TA, 3.3% H₂O₂, 0.36% DTPA, 0.11% MgSO₄, 4.3% Na₂SiO₃),were applied at the eye of the primary refiner. In all the series, thepulp from the primary was allowed 15 minutes retention under cover indrums, (which gave a temperature about 80-90° C.), before the secondstage refining. There was no interstage washing.

[0063]FIG. 2 summarizes some of the process conditions and results fromeach series. The pulps are all from second stage refining. In peroxidebleaching of mechanical pulps, a lower TA/H₂O₂ ratio is in generalpreferred under higher temperature to prevent, or to reduce thepossibility of alkali darkening reaction. For this reason, as shown inTable 1, the lowest TA/H₂O₂ ratio, 1.27, was use for “Refiner” series,the second lowest, 1.31, for “Chip+Refiner” series, and the highest,1.37, for “Chip” series. In “Refiner” series, a larger amount of TAcharge (4.2%) was used to prevent pH from dropping too fast and too lowduring refining because of the high temperature and the heat generatedfrom refining energy. Reasonable amounts of residual peroxide and pHwere maintained in each of the series, FIG. 2.

[0064] As to the chemistry, the main difference between “Chip” and“Chip+Refiner” series is that the latter is more aggressive in movingmore alkaline peroxide chemicals to the refiner chemical treatmentstage.

[0065] Graphic presentation of the data gathered from pulp aftersecondary refining after different investigated processes are shown inFIGS. 3 through 8. FIG. 3 shows effects of the different chemicalapplications on pulp freeness development in relation to specific energyconsumption (SEC), which includes energy consumed during chippretreatment stage. The “Chip+Refiner” series used slightly less SECthan the “Chip” series, but both series used, on average, approximately200 kwh/odmt less SEC than the refiner bleaching series, “Refiner”, eventhough the latter had more caustic chemicals applied than the first twoseries and has the same residual pH, 8.2, as “Chip+Refiner” series. Itappears that adding the alkaline chemical under high temperature, atrefiner eye, causes more alkali consumed on nonproductive, or sidereactions that have little to do with pulp property development.

[0066] It should be pointed out that in a commercial operation, the SECin general is lower than that observed at the lab for chemicalmechanical pulping of hardwoods. The SEC values in FIG. 3, therefore,are better used for comparison purpose than for their absolute values.

[0067] Because many pulp properties, especially the strength properties,are dependent on handsheet density, this property was also analyzedunder SEC, and results are shown in FIG. 4. In this case, the moreaggressive refiner chemical treatment P-RC APMP series, “Chip+Refiner”,had the best efficiency for handsheet density development, which wasfollowed by “Chip” and “Refiner” series. These results demonstrate thatin chemical mechanical pulping, process energy efficiency depends notonly on how much but also on how the chemicals are applied.

[0068] As for pulp intrinsic property development, there was however,little difference among the three series, as illustrated in FIGS. 5 and6, suggesting that as long as the chemicals are added before refining,the mechanism involved in fiber strength property development remainsthe same.

[0069] As for pulp optical property development, in mechanical pulping,pulp brightness is often freeness-dependent. FIG. 7 shows brightness atdifferent freeness from each series. Of interest is that “Chip+Refiner”series had a similar brightness development as that of the “Refiner”series, even though the former used less amount of the bleachingchemicals, 2.6% H₂O₂/3.4% TA versus 3.3% H₂O₂/4.2% TA. Adding all of thechemicals at the impregnation stage, “Chip” series, showed also a lessbleaching efficiency, 2 or more points lower, than that of“Chip+Refiner” series. This suggests that the bleaching efficiency issensitive to how the chemicals are distributed between the chipimpregnation and refining in P-RC APMP process. In this case, acompromise between adding all of the chemicals at chip impregnation orat eye of refiner appears to be the most efficient in bleaching andperoxide consumption.

[0070]FIG. 8 shows that there was no difference in light scatteringproperty development in all the series studied, suggest the pulp surfacedevelopment mechanism also remain the same as long as the chemicals areadded before refining.

EXAMPLE SET B

[0071] The below examples illustrate a different refining configurationwhere the primary refiner was maintained at a negligible gauge pressureat the inlet and a low pressure (approximately 140 kPa) at the casing.Advantages of this configuration include:

[0072] 1) better steam handling at the refiner discharge, especially forhigh capacity refiners (300 t/d or higher);

[0073] 2) ease of transfer primary pulp from the refiner to theinterstage high consistency (HC) tower;

[0074] 3) a potential to use some of the steam generated from theprimary refining (by using a cyclone to separate steam and pulp fiber);

[0075] 4) ease of converting existing TMP systems into a P-RC APMPprocess.

[0076] These examples show that running the primary refiner at a lowpressure (140 kPa) in the casing and atmospheric at the inlet can givesimilar bleaching efficiency as that of atmospheric at both the inletand the casing. Temperatures at the inlet and between the plates in theprimary refiner may push the chromophore removal and hemicellulosealkali hydrolysis reactions fast enough that pH was lowered considerablybefore the pulp reaches the casing out off the refiner plates. The pulpsat the cyclone discharge from the primary refiner were measured in theexamples below to have pH of 9.3-9.7, at which peroxide is easy tostabilize even under the high temperatures (80-90° C.) observed.

[0077] The materials and conditions for the following examples belowwere as follows:

[0078] Wood: Aspen and birch chips from a commercial pulp mill ineastern Canada were used in this study.

[0079] Chip Impregnation: A conventional pilot chip impregnation systemwas used in this study. In all the P-RC APMP runs studied, only DTPA wasused in the first stage of chip impregnation. The chips were thenimpregnated with alkaline peroxide (AP) chemicals at second stageimpregnation. The AP treated chips were then allowed for 30 to 45minutes' retention (without steaming) before being refined.

[0080] Atmospheric Refiner System: Andritz 36″ diameter (92 cm) doubledisc 401 system is typically used for conventional P-RC APMP processinvestigations. This system consists of an open metering belt, anincline twin-screw feeder, the refiner and an open belt discharge. Thesystem is used for both primary and later stages of refining. When usedfor the primary, the pulp discharged were collected in drums and keptunder cover to maintain a high temperature (typically 80 to 90° C.) fora certain period of time.

[0081] Pressurized Refiner System: An Andritz single disc 36″ diameter(92 cm) pressurized system was modified for atmosphericinlet/pressurized casing configuration. The original refiner system hasall the standard features of a conventional TMP system. In order to runthe system with atmospheric pressure at the inlet, a valve was placed ontop of the vertical steaming tube and was kept open during refining.During the trial, the plug screw feeder (PSF) was run at 50 rpm (normalspeed for TMP is 10 to 20 rpm) to ensure the chemical impregnated chipswere not compressed. The AP impregnated chips were placed in a chip bin,which discharged the chips into a blower. The chips were then blown to acyclone and discharged to a conveyor, which feeds the PSF. The chipswere then dropped into a vertical steam tube before being fed into therefiner. During refining, the primary refiner was controlled to havezero pressure at the inlet and 140 kPa in the casing. From the casing,the primary pulp was blown to a cyclone and discharged and collected indrums, and then treated similarly as in the atmospheric refining runs.

[0082] Pulp Tests: TAPPI standard was used for brightness tests.Peroxide residuals were measured using standard iodometric titration.

[0083] Running the primary refiner with pressurized casing andatmospheric inlet was compared with conventional atmospheric refining inP-RC APMP pulping of aspen and birch commercial wood chips. The resultsshowed that both refining configurations gave similar bleachingefficiency. For some installations, using pressurized casing cansignificantly simplify the process, engineering and operation of P-RCAPMP process.

[0084]FIG. 9 presents the chemical conditions used for P-RC APMP pulpingof aspen, and brightness results from atmospheric and casing pressurizedruns with the primary refiner. Applying similar AP chemical strategiesin both cases, and having similar amounts of total chemical consumption(5.2 to 5.4% total alkali, TA, and 3.7 to 3.9% H₂O₂), both theatmospheric and the casing pressurized gave a similar brightness,achieving 84.2% ISO and 84.7% ISO respectively.

[0085] The residual pH (8.8-9.0) in both cases were slightly higher thanideal (approximately 7.0-8.5) and the H₂O₂ residual (1.5 to 2.0% on o.d.pulp) was also higher than normal (0.5 to 1.0%), suggesting that in bothcases the pulp property could be further developed had the chemicaltreatments been further optimized.

[0086] It is worth pointing out that the bleaching efficiency shown inTable 1 (3.7 to 3.9% H₂O₂ and 5.2-5.4% TA consumption to reach 84.2 to84.7% ISO brightness) is comparable to or better than bleachingefficiency normally observed in H₂O₂ bleaching of TMP or CTMP pulps fromaspen.

[0087]20FIG. 10 presents conditions and results from P-RC APMP pulpingof the birch. This particular birch chips was slightly more difficult tobleach than the aspen. Using similar AP chemical strategies, theatmospheric and the pressurizing casing again gave similar bleachingefficiency: 3.1-3.2% TA and 3.4-3.6% H₂O₂ to reach 82.4 to 82.6% ISObrightness. In this case, the residual chemicals (0.1-0.2% TA, 0.5-0.6%H₂O₂ and pH of 8) were within ideal H₂O₂ bleaching conditions.

EXAMPLE SET C

[0088] This example set shows, among other things, that when thechemical recipe and distributions are optimized, the alkali peroxidechemicals at refiner chemical treatment stage can be applied at theintermediate line in a pressurized refiner system to achieve similarbleaching efficiency as P-RC APMP with conventional atmospheric inletpressure. Because the residence time is very short in a intermediateline, the same process may also be used in a high pressure refiningsystem, for example a refining system operating at 4 bar or higher.

Wood

[0089] All the hardwoods (birch and maple) were received in chip formand mixed separately before being further processed. All the softwoods(spruce, pine and softwood blends) were received in log form, anddebarked, chipped and mixed prior to further processing.

Chip Impregnation

[0090] The wood chips, unless otherwise specified, were impregnatedtwice with AP chemicals (consisting of sodium hydroxide (NaOH), hydrogenperoxide (H₂O₂), DTPA, Magnesium Sulfate (MgSO₄) and sodium silicate(Na₂SiO₃), utilizing an Andritz 560GS Impressafiner System. In somecases, the RT-Pressafiner was used at the first stage impregnation(steamed at 1.4 bar for 20 seconds before being pressed).

Refining

[0091] An Andritz 36″ diameter (91 cm) single disc 36-1CP refiner systemwas used for all pressurized and atmospheric inlet/casing pressurizedruns, and an Andritz 36″ diameter (91 cm) double disc 401 system wasused for all atmospheric refining runs. Typically, except where statedotherwise, the 401 refiner was used for all secondary and tertiaryrefining.

Process Description

[0092] The P-RC, (Preconditioning, following by Refiner Chemicaltreatment, where AP chemicals are distributed between chip pretreatmentand refining stages), process was used in all trial runs. For the runswhere AP chemicals were charged at the intermediate line, the pulpdischarged from the blow line was covered under a plastic bag in drumsto maintain a temperature of 85-95° C., depending specific refiningenergy used at the refiner, the chemical charges, and the nature of theraw materials.

Pulp Tests

[0093] Canadian Standard Freeness (CSF) was used for all freeness testsand standard Tappi methods were used for all optical property tests(brightness Tappi T218 OM-83, light scattering, and light absorptioncoefficient Tappi T425 OM-86 (for handsheet Tappi 205 OM-88)).

[0094]FIG. 15 shows the results obtained by applying AP chemicals ateither the refiner eye or the intermediate line during the refinerchemical (RC) treatment stage. Birch and maple woods were used in thisexample. For each wood species, some chemical pretreatment,(preconditioning), was applied on the chips. For birch the chips weretreated with 0.3% DTPA at first stage impregnation, and then 0.2% MgSO₄,4.4% Silicate, 2.8% TA, and 2.8% H₂O₂ at the second stage impregnation.For maple the chips were treated with 0.5% DTPA at first stageimpregnation, and then 0.2% DTPA, 0.1% MgSO₄, 2.0% Silicate, 1.6% TA and2.6% H₂O₂ at the second stage impregnation. The preconditioned chipsthen received a similar amount of AP chemicals during refiner chemical(RC) treatment stage, but at different points: one at the refiner eyebefore refining, and another at the intermediate line immediately afterrefining.

[0095] For the birch, both series (A1 and A2) used a total of 5.2% H₂O₂and 4.6% total alkali (TA), and had a similar amount of H₂O₂ residuals(1.0%-1.1%) and final pH (8.9-9.0). The final pH's were relatively high,indicating that a higher brightness would be achieved if a longerretention time was used. The series from AP addition at the refiner eye(A1) had a similar brightness to samples where AP chemicals were addedat the intermediate line, A2, for example, 84.8 versus 84.2% ISO. Theslight difference in the brightness was likely, at least in part, due tothe slight difference in their freeness, 285 mL for the former case and315 ml for the latter. In terms of chemistry, both series gave similarlight absorption coefficients, 0.27 m²/kg from the former and 0.25 m²/kgfrom the latter.

[0096] In the case of the maple wood, adding AP chemicals atintermediate line, A4, actually gave a higher brightness, 81.9% ISO,than that, 79.2% ISO, from applying the AP chemicals at refiner eye, A3.The difference in this case was a combination of the lower freeness,(295 vs. 320 mL), and the lower light absorption coefficient, (0.32 vs.0.5 m²/kg), of the former.

[0097] Softwoods, namely spruce and red pine, were also investigated into examine effects of different AP chemical applications. FIG. 16summarizes the results, and shows again that similar brightness wasachieved by applying AP chemicals at either the refiner eye or theintermediate line. In the case of spruce the chips were firstimpregnated with 0.3% DTPA, 0.05% MgSO₄, 0.7% Silicate, 0.2% TA and 0.5%H₂O₂, and then 0.1% DTPA, 0.08% MgSO₄, 1.8% Silicate, 1.4% TA and 1.9%H₂O₂ at second stage impregnation.. In the case of red pine the chipswere treated with 0.4% TA, 0.5% H₂O₂, 0.2% DTPA, 0.04% MgSO₄ and 0.5%Silicate at first impregnation, and 0.4% TA, 0.6% H₂O₂, 0.14% DTPA,0.05% MgSO₄, 0.4% Silicate at second stage impregnation. For spruce,using similar amounts of AP chemicals, for example see FIG. 16, the blowline series, A6, had a similar or slightly higher brightness of, 78.8%ISO, than the, 78.2% ISO, from the series, A5, where the last stage ofAP chemicals were applied at the refiner eye. This slight difference ofbrightness again was likely a result of combined effects from theirslightly different freeness, 47 mL vs. 49 mL, and slightly differentlight absorption coefficient, 0.56 vs. 0.60 m²/kg.

[0098] In the case of red pine, the blow line series, A8, had a slightlyhigher brightness, 71.8 vs. 71.2% ISO, lower light absorptioncoefficient, 0.84 vs. 1.01 m²/kg, but higher freeness, 99 vs. 82 mL,compared to the refiner eye series, A7. As far as its effect onbrightness is concerned, in this case, the difference in the lightabsorption coefficient was likely the difference in their freeness. Theamounts of AP chemical treatment were the same for both series.

[0099] A softwood blend from spruce and pine was subjected to highpressure refining at the refiner chemical treatment stage as in FIG. 17.

[0100] In this case, a RT-Pressafiner was used at the first stageimpregnation, and Andritz Model 560GS Impressafiner at the second stage.For this chemical treatment 0.4% TA, 0.6% H₂O₂, 0.18% DTPA, 0.03% MgSO₄and 0.3% Sodium Silicate at 1^(st) stage chip impregnation; 0.4% TA,0.7% H₂O₂, 0.15% DTPA, 0.05% MgSO₄ and 0.4% Sodium Silicate at 2^(nd)stage chip impregnation; 0.9% TA, 1.5% H₂O₂, 0.18% DTPA, 0.09% MgSO₄ and1.8% Sodium Silicate at refiner chemical treatment stage, either at therefiner eye as for A9, or the intermediate line as for A10 was used.Series, A9, A10, were performed, and both had similar chemical chargesand recipe, but one (A9) had 2.1 bar pressure in the primary refiner andthe other, A10, 4.2 bar. FIG. 17 presents results, and shows that theseries with the higher pressure, A10, was able to achieve similarbleaching efficiency and brightness (using 1.7% TA and 2.8% H₂O₂ andreached 73.7-73.4% ISO). The samples had similar light absorptioncoefficient (0.96-1.1 m²/kg). These results indicate that when thechemical strategies were optimized, a similar bleaching efficiency andbrightness (at least in the range of 70-75% ISO) can be achieved at evena very high pressure (4.2 bar, or 60 psi). The high pressure refiningwould make it possible to recover high quality steam with betterefficiency than the lower pressures, and provide an opportunity toreduce shives (fiber bundles) for high freeness pulps.

What is claimed is:
 1. An alkaline peroxide mechanical pulping processcomprising the steps of: feeding a lignocellulosic material into a firstpress; pressing the lignocellulosic material; discharging thelignocellulosic material from the first press; impregnating thelignocellulosic material discharged from the first press with a firstalkaline peroxide pretreatment solution and maintaining the impregnationfor a first reaction time; feeding the impregnated lignocellulosicmaterial to a refiner having an inlet and a rotating disc within asuperatmospheric casing; refining the impregnated lignocellulosicmaterial to form a primary pulp having a temperature of at least about80 C; delivering a stream of primary pulp from the superatmosphericcasing to an intermediate line while the primary pulp temperature is atleast about 80 C; adding an alkaline peroxide intermediate line solutionto the stream of primary pulp within the intermediate line while theprimary pulp temperature is at least about 80 C; mixing the intermediateline solution and the stream of primary pulp to form a reaction mixturein the intermediate line; discharging the reaction mixture having atemperature of at least about 80 C into a retention vessel; retainingthe reaction mixture in the retention vessel to produce a bleachedmaterial.
 2. The alkaline peroxide mechanical pulping process of claim 1further comprising; feeding the lignocellulosic material that has beenimpregnated with the first pretreatment solution for a first reactiontime, into a second press; pressing and discharging the lignocellulosicmaterial from the second press; impregnating the lignocellulosicmaterial discharged from the second press with a second alkalineperoxide pretreatment solution and maintaining the second impregnationfor a second reaction time.
 3. The alkaline peroxide mechanical pulpingprocess of claim 1 further comprising adding an alkaline peroxiderefiner solution to the lignocellulosic material at the refiner.
 4. Thealkaline peroxide mechanical pulping process of claim 1, wherein thestep of feeding the impregnated lignocellulosic material to a refinerhaving an inlet and a rotating disc within a superatmospheric casingincludes maintaining the superatmospheric casing at a pressure of atleast about 240 kPa.
 5. The alkaline peroxide mechanical pulping processof claim 1, wherein the step of mixing is immediately followed byintroducing the mixture into a separator and the separated pulp is thendischarged into said retention vessel.
 6. The alkaline peroxidemechanical pulping process of claim 1, wherein the step of adding analkaline peroxide intermediate line solution to the stream of primarypulp within the intermediate line includes adding the intermediate linesolution immediately after a blow valve.
 7. The alkaline peroxidemechanical pulping process of claim 5, wherein the step of adding analkaline peroxide intermediate line solution to the stream of primarypulp within the intermediate line includes adding the intermediate linesolution immediately prior to the separator.
 8. The alkaline peroxidemechanical pulping process of claim 1, wherein the step of delivering astream of primary pulp from the superatmospheric casing to aintermediate line further includes the primary pulp having a temperaturein the range of about 90 C to about 155 C and a consistency of about 20to about 60%.
 9. The alkaline peroxide mechanical pulping process ofclaim 1, wherein the reaction mixture is retained in the retentionvessel at a temperature of about 60 C to about 95 C and a consistency ofabout 20% to about 40%.
 10. The alkaline peroxide mechanical pulpingprocess of claim 1, wherein the reaction mixture is retained in theretention vessel at a temperature of about 85 C to about 95 C, and aconsistency of about 30%.
 11. The alkaline peroxide mechanical pulpingprocess of claim 1, wherein the impregnation solution contains alkali,peroxide, and stabilizer; the intermediate line solution containsalkali, peroxide, and stabilizer; and said intermediate line solutionhas a temperature less than about 80 C.
 12. The alkaline peroxidemechanical pulping process of claim 2, wherein the first impregnationsolution contains 0.3% DTPA; the second impregnation solution contains0.2% MgSO₄, 4.4% silicate, 2.8% TA, and 2.8% H2O2; and the intermediateline solution contains 0.16% DTPA, 0.16% MgSO4, 2.3% silicate, 1.8% TAwith 0.5% being residual, 2.4% H2O2 with 1.1% being residual.
 13. Thealkaline peroxide mechanical pulping process of claim 2, wherein thefirst impregnation solution contains 0.5% DTPA; the second impregnationsolution contains 0.2% DTPA, 0.1% MgSO4, 2.0% silicate, 1.6% TA, and2.6% H2O2; and the intermediate line solution contains 0.13% DTPA, 0.13%MgSO4, 2.5% silicate, 1.2% TA with 0.1% being residual, 2.1% H2O2 with2.1% being residual.
 14. The alkaline peroxide mechanical pulpingprocess of claim 2, wherein the first impregnation solution contains0.3% DTPA, 0.05% MgSO4, 0.7% silicate, 0.2% TA, and 0.5% H2O2; thesecond impregnation solution contains 0.1% DTPA, 0.08% MgSO4, 1.8%silicate, 1.4% TA, and 1.9% H2O2; and the intermediate line solutioncontains 0.22% DTPA, 0.11% MgSO4, 1.1% silicate, 0.9% TA with 0.2% beingresidual, 1.2% H2O2 with 1.7% being residual.
 15. The alkaline peroxidemechanical pulping process of claim 2, wherein the first impregnationsolution contains 0.4% TA, 0.5% H2O2,0.2% DTPA, 0.04% MgSO4, 0.5%silicate; the second impregnation solution contains 0.14% DTPA, 0.05%MgSO4, 0.5% silicate, 0.4% TA, and 0.6% H2O2; and the intermediate linesolution contains 0.18% DTPA, 0.06% MgSO4, 1.8% silicate, 1.2% TA with0.1% being residual, 1.8% H2O2 with 1.1% being residual.
 16. Thealkaline peroxide mechanical pulping process of claim 2, wherein thefirst impregnation solution contains 0.4% TA, 0.6% H2O2,0.18% DTPA,0.03% MgSO4, 0.3% silicate; the second impregnation solution contains0.15% DTPA, 0.05% MgSO4, 0.4% silicate, 0.4% TA, and 0.7% H2O2; and theintermediate line solution contains 1.7% TA, and 2.8% H2O2 with 1.1%being residual.
 17. A chemimechanical pulping process comprising thesteps of: feeding a lignocellulosic material into a first press;pressing the lignocellulosic material; discharging the lignocellulosicmaterial from the first press; impregnating the lignocellulosic materialdischarged from the first press with a first chemical bleachingpretreatment solution and maintaining the impregnation for a firstreaction time; feeding the lignocellulosic material impregnated with thefirst pretreatment solution to a refiner having an inlet and a rotatingdisc within a superatmospheric casing; refining the lignocellulosicmaterial to form a primary pulp having a temperature of at least 80 C;while the primary pulp temperature is at least about 80 C, dischargingthe primary pulp from the casing to an intermediate line; while theprimary pulp temperature is at least about 80 C, adding an alkalineperoxide intermediate line solution at the intermediate line whichcontains the primary pulp; mixing the intermediate line solution withthe primary pulp; while the intermediate line solution and primary pulpmixture are at a temperature of at least about 80 C discharging theintermediate line solution and primary pulp mixture into a retentiontower; retaining the mixture in the retention tower; and processing theprimary pulp further to a secondary pulp.
 18. An alkaline peroxidemechanical pulping process comprising the steps of: in a primary refinerhaving a superatmoshperic casing, refining a lignocellulosic materialthat has been pretreated and impregnated with at least a first alkalineperoxide pretreatment solution; discharging the lignocellulosic materialat temperature of at least about 80 C into intermediate line having atleast one solution inlet port; injecting an alkaline peroxideintermediate line solution through the at least one solution inlet port;mixing the intermediate line solution and the lignocellulosic materialin the intermediate line; discharging the lignocellulosic material fromthe intermediate line at a temperature of at least about 80 C; andmaintaining the discharged lignocellulosic material for a reactionperiod.
 19. The alkaline peroxide mechanical pulping process of claim18, wherein the step of refining further includes adding a refinersolution of alkaline peroxide at the primary refiner.
 20. The alkalineperoxide mechanical pulping process of claim 18, wherein the step ofinjecting an alkaline peroxide intermediate line solution through the atleast one solution inlet port and into the intermediate line containingthe lignocellulosic material includes injecting an alkaline peroxideintermediate line solution through, at least, one solution inlet portlocated immediately after the blow valve.
 21. An alkaline peroxidemechanical pulping process comprising the steps of: feeding alignocellulosic material into a first press; pressing thelignocellulosic material; discharging the lignocellulosic material fromthe first press; impregnating the lignocellulosic material dischargedfrom the first press with a first alkaline peroxide pretreatmentsolution and maintaining the impregnation for a first reaction time;feeding the impregnated lignocellulosic material to a refiner having aninlet and a rotating disc within a superatmospheric casing; refining theimpregnated lignocellulosic material to form a primary pulp; dischargingthe stream of primary pulp from the superatmospheric casing to anintermediate line; adding an alkaline peroxide intermediate linesolution to the stream of primary pulp within the intermediate line;mixing the intermediate line solution and the stream of primary pulp toform a reaction mixture; discharging the reaction mixture into aretention vessel; retaining the reaction mixture in the retention vesselto produce a bleached material.
 22. The alkaline peroxide mechanicalpulping process of claim 21, further comprising; feeding thelignocellulosic material that has been impregnated with the firstpretreatment solution for a first reaction time, into a second press;pressing and discharging the lignocellulosic material from the secondpress; impregnating the lignocellulosic material discharged from thesecond press with a second alkaline peroxide pretreatment solution andmaintaining the second impregnation for a second reaction time.
 23. Thealkaline peroxide mechanical pulping process of claim 21 furthercomprising adding an alkaline peroxide refiner solution to thelignocellulosic material at the refiner.
 24. The alkaline peroxidemechanical pulping process of claim 21, wherein the step of dischargingthe stream of primary pulp from the superatmospheric casing to anintermediate line includes the intermediate line having a blow valve andadding the alkaline intermediate line solution immediately after theblow valve.
 25. The alkaline peroxide mechanical pulping process ofclaim 21, wherein discharging the stream of primary pulp from thesuperatmospheric casing includes the intermediate line having a blowvalve followed by a separator and the step of adding an alkalineperoxide intermediate line solution to the stream of primary pulp withinthe intermediate line includes adding the alkaline peroxide intermediateline solution immediately prior to the separator.
 26. The alkalineperoxide mechanical pulping process of claim 21, wherein discharging thestream of primary pulp from the superatmospheric casing includes theintermediate line having a blow valve followed by a separator and thestep of adding an alkaline peroxide intermediate line solution to thestream of primary pulp within the intermediate line includes adding thealkaline peroxide intermediate line solution at the separator.
 27. Thealkaline peroxide mechanical pulping process of claim 24, whereindischarging the stream of primary pulp from the superatmospheric casingincludes the intermediate line having a blow valve followed by aseparator and the step of adding an alkaline peroxide intermediate linesolution to the stream of primary pulp within the intermediate lineincludes adding the alkaline peroxide intermediate line solutionimmediately after the separator.
 28. The alkaline peroxide mechanicalpulping process of claim 21, wherein the step of feeding the impregnatedlignocellulosic material to a refiner having an inlet and a rotatingdisc within a superatmospheric casing includes maintaining thesuperatmospheric casing at a pressure of at least about 240 kPa.
 29. Thealkaline peroxide mechanical pulping process of claim 21, wherein theimpregnation solution contains alkali, peroxide, and stabilizer; theintermediate line solution contains alkali, peroxide and stabilizer; andsaid intermediate line solution is at a temperature less than the streamof primary pulp.
 30. The alkaline peroxide mechanical pulping process ofclaim 22, wherein the first impregnation solution contains 0.3% DTPA;the second impregnation solution contains 0.2% MgSO4, 4.4% silicate,2.8% TA, and 2.8% H2O2; and the intermediate line solution contains0.16% DTPA, 0.16% MgSO4, 2.3% silicate, 1.8% TA with 0.5% beingresidual, 2.4% H2O2 with 1.1% being residual.
 31. The alkaline peroxidemechanical pulping process of claim 22, wherein the first impregnationsolution contains 0.5% DTPA; the second impregnation solution contains0.2% DTPA, 0.1% MgSO4, 2.0% silicate, 1.6% TA, and 2.6% H2O2; and theintermediate line solution contains 0.13% DTPA, 0.13% MgSO4, 2.5%silicate, 1.2% TA with 0.1% being residual, 2.1% H2O2 with 2.1% beingresidual.
 32. The alkaline peroxide mechanical pulping process of claim22, wherein the first impregnation solution contains 0.3% DTPA, 0.05%MgSO4, 0.7% silicate, 0.2% TA, and 0.5% H2O2; the second impregnationsolution contains 0.1% DTPA, 0.08% MgSO4, 1.8% silicate, 1.4% TA, and1.9% H2O2; and the intermediate line solution contains 0.22% DTPA, 0.11%MgSO4, 1.1% silicate, 0.9% TA with 0.2% being residual, 1.2% H2O2 with1.7% being residual.
 33. The alkaline peroxide mechanical pulpingprocess of claim 22, wherein the first impregnation solution contains0.4% TA, 0.5% H2O2,0.2% DTPA, 0.04% MgSO4, 0.5% silicate; the secondimpregnation solution contains 0.14% DTPA, 0.05% MgSO4, 0.5% silicate,0.4% TA, and 0.6% H2O2; and the intermediate line solution contains0.18% DTPA, 0.06% MgSO4, 1.8% silicate, 1.2% TA with 0.1% beingresidual, 1.8% H2O2 with 1.1% being residual.
 34. The alkaline peroxidemechanical pulping process of claim 22, wherein the first impregnationsolution contains 0.4% TA, 0.6% H2O2,0.18% DTPA, 0.03% MgSO4, 0.3%silicate; the second impregnation solution contains 0.15% DTPA, 0.05%MgSO4, 0.4% silicate, 0.4% TA, and 0.7% H2O2; and the intermediate linesolution contains 1.7% TA, and 2.8% H2O2 with 1.1% being residual.
 35. Achemimechanical pulping process comprising the steps of: feeding alignocellulosic material into a press; pressing the lignocellulosicmaterial; discharging the lignocellulosic material from the press;impregnating the lignocellulosic material discharged from the press witha chemical bleaching pretreatment solution; feeding the lignocellulosicmaterial impregnated with the pretreatment solution to a refiner havingan inlet and a rotating disc within a superatmospheric casing; refiningthe lignocellulosic material to form a primary pulp; discharging theprimary pulp from the casing through an intermediate line; adding analkaline peroxide solution at the intermediate line to the primary pulp;mixing the intermediate line solution with the primary pulp; deliveringthe intermediate line solution and primary pulp mixture to a retentiontower; processing the primary pulp from the retention tower, into asecondary pulp.
 36. An alkaline peroxide mechanical pulping processcomprising the steps of: in a primary refiner having a superatmoshpericcasing, refining a lignocellulosic material that has been pretreated andimpregnated with at least a first alkaline peroxide pretreatmentsolution; discharging the lignocellulosic material into an intermediateline having at least one solution inlet port; injecting an alkalineperoxide intermediate line solution through the at least one solutioninlet port; mixing the intermediate line solution and thelignocellulosic material; discharging the lignocellulosic material fromthe intermediate line; and retaining the discharged lignocellulosicmaterial for a reaction period.
 37. The alkaline peroxide mechanicalpulping process of claim 36, wherein the step of refining furtherincludes adding a refiner solution of alkaline peroxide at the primaryrefiner.
 38. The alkaline peroxide mechanical pulping process of claim36, wherein the step of injecting an alkaline peroxide intermediate linesolution through the, at least one, solution inlet port and into theintermediate line containing the lignocellulosic material includesinjecting an alkaline peroxide intermediate line solution through, atleast, one solution inlet port located immediately after a blow valve.39. The alkaline peroxide mechanical pulping process of claim 36,wherein the step of injecting an alkaline peroxide intermediate linesolution through the, at least one, solution inlet port and into theintermediate line containing the lignocellulosic material includesinjecting an alkaline peroxide intermediate line solution through, atleast, one solution inlet port located immediately prior to a separator.40. The alkaline peroxide mechanical pulping process of claim 36,wherein the step of injecting an alkaline peroxide intermediate linesolution through the, at least one, solution inlet port and into theintermediate line containing the lignocellulosic material includesinjecting an alkaline peroxide intermediate line solution through, atleast, one solution inlet port located at a separator.
 41. The alkalineperoxide mechanical pulping process of claim 36, wherein the step ofinjecting an alkaline peroxide intermediate line solution through the,at least one, solution inlet port and into the intermediate linecontaining the lignocellulosic material includes injecting an alkalineperoxide intermediate line solution through, at least, one solutioninlet port located at a discharge portion of a separator.
 42. Analkaline peroxide mechanical pulping process comprises the steps of: ina refiner having a casing, additionally refining a lignocellulosic basedmaterial that has been previously pretreated and impregnated with atleast a first alkaline peroxide pretreatment solution and which has beenpreviously refined; discharging the lignocellulosic based material intoan intermediate line having at least one solution inlet port; injectingan alkaline peroxide intermediate line solution through the at least onesolution port; mixing the intermediate line solution and thelignocellulosic based material; discharging the lignocellulosic basedmaterial from the intermediate line; and retaining the dischargedlignocellusic based material for a reaction period.
 43. The alkalineperoxide mechanical pulping process of claim 42, wherein the refinercasing is superatmospheric.